Efficient screening rooted in a series of transition-metal atom-anchored conjugated organic frameworks toward multifunctional HER/OER/ORR via the modification of chalcogen ligands: a machine learning and constant potential study

Abstract

The pursuit of two-dimensional single-atom catalysts (SACs) is of significant importance for advancing the energy conversion and storage technologies by providing efficient, stable, and low-cost alternatives for precious metals in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). The synergy between tunable ligands, abundant transition metal active sites, and diverse substrate materials facilitate in attaining both stability and enhanced catalytic activity. This study provides a thorough examination of the catalytic HER/OER/ORR activities in 161 TM@C₁₅N₆XY₂H₅ SACs, combining density functional theory with machine learning (ML). Thirteen configurations were identified, comprising 11 single-function OER/ORR catalysts, a bifunctional OER/ORR catalyst, namely Cu@C₁₅N₆O₃H₅, and Au@C₁₅N₆OS₂H₅, which demonstrated trifunctional HER/OER/ORR catalytic activity. A pronounced hybridization between Cu/Au-d orbitals and O-p orbitals of oxygenated adsorbates directs the lone electrons to antibonding states before transitioning to bonding orbitals, enabling efficient adsorption of oxygenated intermediates on the surface. The data obtained through ML applications indicate that the atomic radius (r_TM) and electronegativity (χ) of TM are the primary descriptors for the HER activity, while the d-electron count (θ) and atomic radius (r_TM) of the atoms are the key descriptors for the OER/ORR activities. Through the SISSO method, a clear and robust correlation between intrinsic properties and adsorption energy was derived, enabling predictions at each step. Additionally, the constant-potential model showed that electric double-layer capacitance modulated the reaction barrier; meanwhile, pH- and voltage-dependent adsorption free energies indicated that acidic and alkaline conditions (pH 5.3/9.9, Cu@C₁₅N₆O₃H₅/Au@C₁₅N₆OS₂H₅) enhanced the OER efficiency, while pH 0 is optimal for the ORR.